----- On Jul 2, 2018, at 6:08 PM, Linus Torvalds torvalds@xxxxxxxxxxxxxxxxxxxx wrote:
> On Mon, Jul 2, 2018 at 3:03 PM Mathieu Desnoyers
> <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>>
>> if (__get_user(ptr, &t->rseq->rseq_cs))
>> return -EINVAL;
>> if (check_rseq_cs_padding(t))
>> return -EINVAL;
>
> Small nit.
>
> I think the _actual_ user access faults should return -EFAULT, and
> then the *validation* checks should return -EINVAL.
>
> So when the "copy_from_user()" fails, that's -EFAULT, but when you
> have (rseq_cs->start_ip >= TASK_SIZE), that's -EINVAL.
Fair enough.
>
> That said, nothing actually cares or exposes the error number, I
> think. Afaik, all the callers just check "did it work" or not.
Indeed, it's a static function and callers just check for zero/nonzero.
>
> So this is more a "let's be consistent" than anything that matters.
Allright, here is the function updated accordingly:
static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
{
struct rseq_cs __user *urseq_cs;
unsigned long ptr;
u32 __user *usig;
u32 sig;
int ret;
ret = __get_user(ptr, &t->rseq->rseq_cs);
if (ret)
return ret;
if (check_rseq_cs_padding(t))
return -EINVAL;
if (!ptr) {
memset(rseq_cs, 0, sizeof(*rseq_cs));
return 0;
}
urseq_cs = (struct rseq_cs __user *)ptr;
if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
return -EFAULT;
if (rseq_cs->start_ip >= TASK_SIZE ||
rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
rseq_cs->abort_ip >= TASK_SIZE ||
rseq_cs->version > 0)
return -EINVAL;
/* Check for overflow. */
if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)
return -EINVAL;
/* Ensure that abort_ip is not in the critical section. */
if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
return -EINVAL;
usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
ret = get_user(sig, usig);
if (ret)
return ret;
if (current->rseq_sig != sig) {
printk_ratelimited(KERN_WARNING
"Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
sig, current->rseq_sig, current->pid, usig);
return -EINVAL;
}
return 0;
}
Thanks for the feedback!
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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